During the mid-1970's there were important unanswered questions relating to the efficacy of very low calorie diets in promoting fat loss. Seeking a method to quantify the small changes in total body fat needed to examine these diets, Drs. Mei Yang and Theodore Van Itallie developed the resources needed to perform energy-nitrogen balance studies at SLRHC. Thermogenesis measurements, food composition analyses, and urine and fecal energy-nitrogen content were all evaluated in their now classic experiment designed to examine body composition changes with dieting (Yang &Van Itallie, 1976). The present Core is an outgrowth of these initial efforts. Subsequent studies of thermogenesis, food intake, and physical activity in obese patients required further expansion of the Center's Body Composition, Physical Performance, and Energy Expenditure Laboratories (Pi-Sunyer &Segal, 1986). This growth provided the setting to critically evaluate such new body composition methodologies as total body electrical conductivity (Van Itallie et al, 1985), bioimpedance analysis (BIA) (Segal et al, 1985), dual photon/x-ray absorptiometry (DPA/DXA)(Heymsfield et al, AJCN 1989;Wang et al, AJP 1989), and inelastic neutron scattering (Kehayias et al, 1987). Core scientists developed multicomponent body composition methods that exploit these unique body composition methods (Heymsfield et al, 1991). The Core's scientists extended their efforts to imaging (Gallagher et al, 1998;2000) and nuclear magnetic resonance spectroscopy methods (Shen 2007), in collaboration with colleagues in the Department of Bio-engineering and Radiology at Columbia University and in the Department of Radiology at SLRHC. Exploration of weight-related performance issues in the elderly and other groups by Drs. Gallagher (Song et al, 2004;Kim et al, 2003), Geliebter et al, (1997), Kotler (Agin et al, 2001;He et al, 2005) and others led to additional advancements in the Core's Human Physical Performance Laboratory. New, more sensitive, methods for quantifying strength and endurance are now available. In the mid-nineties, imaging methods became a central measurement technique for in vivo body composition analysis. Whole body magnetic resonance imaging (MRI) has now become a state-of-the-art technique among Core investigators (Yim 2007;Shen 2007;Freda 2008;Gallagher 2009, Ochner &Geliebter, 2010;Ochner, In Press). Recent new phenotyping developments include the validation of a 3-dimensional photonic scanner (Wang 2006) for assessment of body volume and fat suitable for use in very large persons;quantification of bone marrow adipose tissue from whole-body MRI scans (Shen et al, 2007);and validation of the Echo QMR for fat and water in humans (Gallagher 2010) where the precision exceeds that of any other available technique, albeit accuracy needs to be improved. With the introduction of new energy expenditure assessment techniques, the core investigators improved the Core Laboratory's thermogenesis measurement capabilities to include ventilated hood indirect calorimetry and the doubly-labeled water technique (analyzed in the CTSA laboratory). Two respiratory chamber-indirect calorimeter systems for measuring 24-hour energy expenditure, one for humans and the other for animals, were developed with collaborating bioengineers at Columbia. The present Human Body Composition Core thus includes extensive capabilities for studying body composition, physical performance, image analysis, and energy expenditure in humans. These facilities, which serve investigators throughout the metropolitan New York area, are based at SLRHC. Cooperating laboratories include The Magnetic Resonance Research Laboratories of Columbia University which include the Departments of Radiology and Psychology Center for Neurobiology and Behavior /MRI Research Center under the direction of Joy Hirsch, PhD, and The Hatch Research Center and the Biomedical Engineering Imaging Research Center under the direction of Truman Brown, PhD, both located in the Neurological Institute, Columbia University Medical Center. Overall, this state-of-the art human body composition Core provides Center investigators with the potential for extending their in vivo analyses to previously unmeasurable body components and compartments. Over the past five years, the Core presence catalyzed collaborative research in the New York metropolitan area at 6 (SLRHC, CU, Weill Cornell, Rockefeller University, Renal Research Institute of New York) institutions plus 3 outside New York (Pennington, U Southern California, U California San Francisco) with 34 investigators using various Core services (see Section 8).